#include <cstdio>
#include <cstring>
#include <cassert>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/wait.h>
#include <iostream>
using namespace std;
#define NUM 1024
#define OPT_NUM 64

#define NONE_REDIR 0
#define INPUT_REDIR 1
#define OUTPUT_REDIR 2
#define APPEND_REDIR 3
#define trimSpace(start)        \
    do                          \
    {                           \
        while (isspace(*start)) \
            ++start;            \
    } while (0);

int lastCode = 0;
int lastSig = 0;

char LineCommand[NUM];
char *myargv[OPT_NUM];

int redirType = NONE_REDIR;
char *redirFile = nullptr;
void commandCheck(char *commands)
{
    assert(commands);
    char *start = commands;
    char *end = start + strlen(commands);
    while (start < end)
    {
        if (*start == '>')
        {
            *start = '\0';
            start++;
            if (*start == '>')
            {
                redirType = APPEND_REDIR;
                start++;
            }
            else
            {
                redirType = OUTPUT_REDIR;
            }
            trimSpace(start);
            redirFile = start;
            break;
        }
        else if (*start == '<')
        {
            *start = '\0';
            start++;
            trimSpace(start);
            redirType = INPUT_REDIR;
            redirFile = start;
            break;
        }
        else
        {
            start++;
        }
    }
}
int main(int argc, char *argv[])
{
    while (1)
    {
        redirType = NONE_REDIR;
        redirFile = nullptr;
        errno = 0;
        printf("用户名@主机名 当前路径# ");
        fflush(stdout);
        char *s = fgets(LineCommand, sizeof(LineCommand) - 1, stdin);
        assert(s != NULL);
        (void)s;
        LineCommand[strlen(LineCommand) - 1] = 0;
        commandCheck(LineCommand);
        myargv[0] = strtok(LineCommand, " ");
        int i = 1;
        if (myargv[0] != nullptr && strcmp(myargv[0], "ls") == 0)
        {
            myargv[i++] = (char *)"--color=auto";
        }
        while (myargv[i++] = strtok(NULL, " "))
            ;
        if (myargv[0] != nullptr && strcmp(myargv[0], "cd") == 0)
        {
            if (myargv[1] != nullptr)
            {
                chdir(myargv[1]);
            }
            continue;
        }
        if (myargv[0] != nullptr && myargv[1] != nullptr && strcmp(myargv[0], "echo") == 0)
        {
            if (strcmp(myargv[1], "$?") == 0)
            {
                printf("%d, %d\n", lastCode, lastSig);
            }
            else
            {
                printf("%s\n", myargv[1]);
            }
            continue;
        }
#ifdef DEBUG
        for (int i = 0; myargv[i]; i++)
        {
            printf("myargv[%d]:%s\n", i, myargv[1]);
        }
#endif
        pid_t id = fork();
        assert(id != -1);
        if (id == 0)
        {
            switch (redirType)
            {
            case NONE_REDIR:
                break;
            case INPUT_REDIR:
            {
                int fd = open(redirFile, O_RDONLY);
                if (fd < 0)
                {
                    perror("open");
                    exit(errno);
                }
                dup2(fd, 0);
            }
            break;
            case OUTPUT_REDIR:
            case APPEND_REDIR:
            {
                umask(0);
                int flags = O_WRONLY | O_CREAT;
                if (redirType == APPEND_REDIR)
                {
                    flags |= O_APPEND;
                }
                else
                {
                    flags |= O_TRUNC;
                }
                int fd = open(redirFile, flags, 0666);
                if (fd < 0)
                {
                    perror("open");
                    exit(errno);
                }
                dup2(fd, 1);
            }
            break;
            default:
                printf("bug?\n");
                break;
            }
            execvp(myargv[0], myargv);
            exit(1);
        }
        int status = 0;
        pid_t ret = waitpid(id, &status, 0);
        assert(ret > 0);
        (void)ret;
        lastCode = ((status >> 8) & 0xFF);
        lastSig = ((status) & 0x7F);
    }
    return 0;
}